Anti-corrosive pigments are used to protect metal surfaces against oxidation and corrosion. Those pigments usually include heavy metals salts, which hinder the rusting of the metal surface by either cathodic or anodic inhibition mechanisms. Upon dissolving in the aqueous phase, commercial available anti-corrosive pigments partially dissolved to provide hydrated metal cation and hydrated anion solutions, which reacts with the metallic surface. The reaction between the partially solubilized pigments provides the desired inhibition of corrosion.
Zinc compounds such as zinc phosphate and zinc chromate are currently widely used as anti-corrosive pigments. Zinc is a heavy metal element and is considered to be toxic at certain concentrations.
Magnesium phosphate salts, and especially tri-basic magnesium phosphate were presented as possible anti-corrosive pigments. U.S. Pat. No. 3,960,611 to Walker discloses a composition for anti-corrosive pigments containing magnesium phosphate. This composition was found to provide only a moderate corrosion inhibition.
The anti-corrosivity of magnesium phosphates was significantly improved by applying molten magnesium salt on the surface of ferric materials.
U.S. Pat. No. 4,411,876 to Sherif, discloses an anti corrosive pigment comprising tri-magnesium phosphate salts. The production of tri-magnesium phosphate salts includes admixing of mono-magnesium phosphate solution with a slurry of magnesium hydroxide in pH below 6.8.
However, it is acknowledged that maintaining of pH higher 9.0 is profitable for corrosion inhibition. A composition that provides for a buffering effect in a basic range is thus preferred.
U.S. Pat. No. 6,331,202 to Applicant discloses anti-corrosive amino-based compositions, including both oxyaminophophate and one selected from oxynitrite, oxymetalphosphate, oxyborate or oxysilicate.
Similarly, U.S. Pat. No. 6,312,812 to Hauser et al. discloses anti-corrosive compositions including both transition elements such as metals, and amine-containing materials.
The object of the invention is to provide a non-toxic anti-corrosive pigment that does not contain heavy metals and perform equally or better then commercial available anti-corrosive pigments.